Two-dimensional mineral hydrogel-derived single atoms-anchored heterostructures for ultrastable hydrogen evolution

Hydrogen energy is critical for achieving carbon neutrality. Heterostructured materials with single metal-atom dispersion are desirable for hydrogen production. However, it remains a great challenge to achieve large-scale fabrication of single atom-anchored heterostructured catalysts with high stability, low cost, and convenience. Here, we report single iron (Fe) atom-dispersed heterostructured Mo-based nanosheets developed from a mineral hydrogel. These rationally designed nanosheets exhibit excellent hydrogen evolution reaction (HER) activity and reliability in alkaline condition, manifesting an overpotential of 38.5 mV at 10 mA cm−2, and superior stability without performance deterioration over 600 h at current density up to 200 mA cm−2, superior to most previously reported non-noble-metal electrocatalysts. The experimental and density functional theory results reveal that the O-coordinated single Fe atom-dispersed heterostructures greatly facilitated H2O adsorption and enabled effective adsorbed hydrogen (H*) adsorption/desorption. The green, scalable production of single-atom-dispersed heterostructured HER electrocatalysts reported here is of great significance in promoting their large-scale implementation.


Supplementary Tables
Supplementary Table 1 Supplementary Fig. 1 The centrifugation approach to the formation of the mineral hydrogel.
As shown in Supplementary Fig. 4, 5a, when the ratio Fe 3+ /PMo is as low as 6:1 forms a sphere-like shape with a diameter of about several hundred nanometers that is comprised of several spheres grown together. When the ratio is increased to 12:1, its morphology consists of uniform nanoparticles that are significantly smaller than that of the 6:1 ( Supplementary Fig. 5b). When the ratio is increased again to 19:1, the morphology is totally different, as depicted in Supplementary Fig. 5c, it seems to form a nanosheet-like cluster, but it is like a rudiment of the whole nanosheet, and in some places, it appears to consist of many agminated nanoparticles covered by a thin film. It's necessary to note that partially deposited on the bottom of the bottle and the upper liquid near to the solution surface became transparent. At a ratio of 25:1, Fe 3+ and PMo obviously self-assembled into wrinkle-like nanosheets ( Supplementary Fig. 5d). At a ratio of 31:1, they self-assembled into a wrinkle nanosheet ( Supplementary Fig. 5e) with a significantly higher thickness than that of 25:1. At a ratio of 37:1, it took much longer to form precipitates, and the nanosheet was very large with vast wrinkles at the surface ( Supplementary Fig. 5f). Too high ratio led to overly lengthy assembly (when the molar ratio of Fe 3+ /PMo was 50:1, not shown here, self-assembly took about seven days), and when the molar ratio of Fe 3+ /PMo was as high as 60:1, the solution kept transparent. It can be concluded from this concentration-dependent experiment that the morphology of the FePMo composites is significantly dependent on the ratio of Fe 3+ to POM, and the higher ratios of Fe 3+ /PMo were associated with a longer self-assembly process.
Supplementary   In the FT-EXAFS spectra and fitting line at Mo K-edge, the peaks at 1. 45        To further explore the strength of bonding between H2O molecules and active sites, we determined the partial density of states (PDOS) curves of Mo/Fe active sites and O atoms in H2O molecules ( Supplementary Fig. 28). As can be seen, the intensities of interaction between the electrons in the s-, p-, d-orbitals of Mo/Fe and the s-, p-orbitals of O are rather different, which accounts for the variation in the H2O adsorption ability of different models. The PDOS peak overlap of Mo and O orbitals is most extensive in MoO2 in the single-phase models, whereas it is most extensive in MoP/MoP2 in the heterostructured interface models. In addition, the PDOS peaks of O perfectly overlap with that of Fe in Fe@MoO2-1 but not in Fe@MoO2-2, which accounts for the significant difference in these species' H2O adsorption ability. These physical insights explain the variation in the electron-transfer ability of different structures, and thus highlight the microstructures that are critical for efficient H2O adsorption. Supplementary Fig. 30 The representative atomic configurations after H adsorption at the surface sites of MoP, MoP2 and MoO2 with corresponding ΔGH*. Supplementary Fig. 31 DFT results of 2D electron density differences after adsorption of H* onto the active sites in the single-phase models. Red and blue represent the depletion and accumulation of electrons with the unit of e/Å 3 , respectively.
In the single-phase models ( Supplementary Fig. 30), it can be seen that electron transfer between H* and Mo is too weak at the Mo top of MoP, given its ΔGH* value of 0.31 eV.
A stronger depletion of electrons in Mo occurs at the Mo-Mo bridge than that at the Mo top, which improves H* adsorption at the surface of MoP; however, this interaction is too strong, resulting in an unsuitable ΔGH* value (-0.35 eV). The electron-transfer ability of the Mo top of MoP2 is similar to that of MoP, which results in a similarly unsuitable ΔGH* value (0.37 eV). The Mo-P bridge in MoP2 shows a slightly stronger interaction with H*, owing to additional electron transfer from P to H*, and thus its ΔGH* value is slightly better (0. To ensure the comparability of d-band centres in active sites, we examined only the same Mo top sites in single-phase and heterostructured interface models: thus, MoP/MoO2 and MoP2/MoO2 interface models with optimal ΔGH* values were compared with the single-phase models Supplementary